A load balancing method and system is provided. When a terminal enters an idle, access or service state, and a base station determines that the terminal is in a multi-band covering section, load conditions of the bands in the section are recorded; and when determining that a preset idle or access or service state condition is met based on the recorded load conditions of the bands in the section, the base station performs load balancing control on the terminal. For the terminal in the idle, access or service state, load balancing for a multi-band network can be implemented.